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The C programming language provides many standard library functions for file input and output.These functions make up the bulk of the C standard library header <stdio.h>. [1] The functionality descends from a "portable I/O package" written by Mike Lesk at Bell Labs in the early 1970s, [2] and officially became part of the Unix operating system in Version 7.
Stream editing processes a file or files, in-place, without having to load the file(s) into a user interface. One example of such use is to do a search and replace on all the files in a directory, from the command line. On Unix and related systems based on the C language, a stream is a source or sink of data, usually individual bytes or characters.
an input stream that wraps a file stream buffer. Provides functions to open or close a file in addition to those of generic input stream ifstream – operates on characters of type char; wifstream – operates on characters of type wchar_t; basic_istringstream: an input stream that wraps a string stream buffer.
Unix eliminated this complexity with the concept of a data stream: an ordered sequence of data bytes which can be read until the end of file. A program may also write bytes as desired and need not, and cannot easily declare their count or grouping.
By default, the driver converts a Control-D character at the start of a line into an end-of-file indicator. To insert an actual Control-D (ASCII 04) character into the input stream, the user precedes it with a "quote" command character (usually Control-V). AmigaDOS is similar but uses Control-\ instead of Control-D.
The byte-order mark (BOM) is a particular usage of the special Unicode character code, U+FEFF ZERO WIDTH NO-BREAK SPACE, whose appearance as a magic number at the start of a text stream can signal several things to a program reading the text: [1] the byte order, or endianness, of the text stream in the cases of 16-bit and 32-bit encodings;
The file is identified by a file descriptor that is normally obtained from a previous call to open. This system call reads in data in bytes, the number of which is specified by the caller, from the file and stores then into a buffer supplied by the calling process. The read system call takes three arguments: The file descriptor of the file.
This is because the redirection form opens the file as the stdin file descriptor which command can fully access, while the cat form simply provides the data as a stream of bytes. Another common case where cat is unnecessary is where a command defaults to operating on stdin, but will read from a file, if the filename is given as an argument.